In the manufacture of garments utilizing automatic sewing machines, it is necessary to provide some sort of a knife assembly in order to cut the leading and/or trailing threads which effect stitching of the garment. Typically a scissors action type cutting element is provided just downstream of the automatic sewing machine throat plate in the direction of garment movement, and a vacuum is utilized to draw the thread into operative association with the scissors type cutter, and then to carry away the cut thread. Utilizing such a conventional structure--standard equipment with Union Special Corporation type sewing machines--cutting may be effectively practiced, however the amount of thread tail remaining is typically on the order of about one inch. Also, in the prior art, the garment itself sometimes is sucked into contact with the knife, resulting in change to the garment or temporary cessation of the cutting action.
According to the present invention, a thread cutting knife assembly for an automatic sewing machine, and in combination with an automatic sewing machine, is provided which allows the leading or trailing thread to be cut much more closely to the garment than in the prior art, the apparatus according to the invention essentially allowing the thread to be cut right at the garment. This very advantageous action is provided by the particular design and orientation of a top plate of the assembly defining a surface over which the thread passes, the particular cutting elements, and the means for effecting air flow.
According to one aspect of the present invention a thread cutting knife assembly for an automatic sewing machine comprises: A top plate defining a surface over which thread passes. The top plate having means defining a groove in the top plate elongated generally in a first dimension. A body member having an open top cavity therein, and a first end and a second end, the first and second ends spaced from and opposite each other in the first dimension [the top plate covers the body member cavity open top]. A movable cutting element elongated in the first dimension, and disposed between the top plate and the body member, having a cutting portion at a first end thereof adjacent the body first end, and an engagable portion at a second end thereof spaced from and opposite the first end in the dimension of elongation. A stationary cutting element positioned closer to the body first end than the top plate is positioned, and disposed over the body cavity. Means for reciprocating the cutting element in the first dimension, the means engaging the engagable portion of the movable cutting element. And, means for effecting air flow within the cavity from the body first end toward the body second end in the first dimension.
The air flow effecting means preferably comprises a flexible material tube extending outside the body from connection to a source of air under pressure adjacent the body second end to a first opening in the first end of the body, so as to provide a flow of air under pressure in the cavity. Moving the thread in a blown stream of air allows better control over the thread than in a purely suction stream. Also, it is desirable to provide a second opening in the first end of the body adjacent the first opening open to the atmosphere so that compressed air passing through the tube entrains atmospheric air which also passes through the cavity under a Venturi effect. This air flow entrains the cut thread, and passes it to a disposal area.
The cutting portion of the movable cutting element preferably makes an angle of about 45.degree.-75.degree. with respect to the first dimension, in the direction from the first end to the second end. Also the body is open at the second end and the means for reciprocating the movable cutting element comprises means defining a passage away from the body in fluid communication with the body second end. For example, the means for reciprocating the cutting element may further comprise a cam engaging element, the passage being defined in the cam engaging element so that it normally moves the first end of the movable cutting element into engagement with the stationary cutting element. The body first end has a termination slanting downwardly from the body cavity open top, and the flexible tube enters the first opening beneath that end termination.
The assembly according to the present invention is preferably part of an automatic sewing machine. That is, according to the invention an automatic sewing machine is provided including a sewing needle, a pressure foot, a throat plate, feed dogs, and a leading or trailing thread cutting knife assembly. The knife assembly is operatively positioned with respect to the sewing needle, pressure foot, throat plate, and feed dogs to receive cloth stitched with thread by the needle, the cloth moving in a first direction in a first dimension with respect to the knife assembly. The knife assembly is as described above. It cooperates with cams also forming part of the automatic sewing machine.
Utilizing the apparatus according to the present invention, less air is needed than in conventional automatic sewing machine cutting mechanisms, and there is better control over the thread in the air stream. Also, a reciprocating action is provided for effecting cutting of the thread rather than a scissors action, which allows a construction that minimizes the cloth entering the cutting mechanism, but maximizes the probability that the thread will be properly positioned for cutting. Utilizing the invention it is possible to trim the thread very close to the leading and trailing edges of the garments, e.g. leaving only a few millimeters of thread tail rather than one inch as in the prior art.
The invention also contemplate a particular pneumatic actuator which may be used to reciprocate the movable cutting element of the knife assembly, or in other circumstances where a pneumatic actuator of a small, predetermined stroke length is desired. The pneumatic actuator according to the invention is for reciprocating a reciprocal element, and comprises the following elements: A body defining an interior cylindrical bore, having means defining an opening therein for introduction of gas under pressure. A piston including a shaft for connection to the reciprocal element, and a piston face which is engaged by gas under pressure, the piston mounted in the cylinder for reciprocal movement therein. Means defining an opening in the piston face, including an interior bore parallel to the cylindrical bore. A stationary rod extending from the body into the piston interior bore. An O-ring having an outside diameter, and compressibility, such that the O-ring can sealingly engage the piston interior bore and prevent gas from passing therepast. Means for mounting the O-ring with respect to the piston so that O-ring moves with the piston, providing a gas-tight seal preventing gas from the cylindrical bore opening passing into the piston interior bore, a first distance, and after the O-ring and piston have moved together the first distance the piston continues to move while the O-ring does not so that there is relative movement therebetween and the seal between the O-ring and the piston interior bore is broken, and gas from the cylindrical bore opening may freely pass into the piston interior bore; and vent means for venting gas passing into the piston interior bore.
Preferably the means for mounting the O-ring comprises a rod fixed to the body and extending into the piston interior bore, substantially parallel to the cylindrical bore. The rod has a shoulder which acts on the O-ring to instigate the relative movement between the O-ring and piston, and the vent means comprises means defining an opening in the rod, and an interior passageway in the rod extending to a point in operative communication with the exterior of the body. Desirably, spring means are provided for biasing the O-ring on the rod in a direction opposite the direction of movement thereof with the piston in response to gas under pressure being introduced into the cylinder, and spring means are also provided for biasing the piston in a direction opposite to the direction of movement thereof in response to gas under pressure being introduced into the cylinder.
It is the primary object of the present invention to provide for the effective trimming of thread from the leading and/or trailing edges of garments stitched by an automatic sewing machine. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.